1. Field of the Invention
The present invention relates to an electronic component, a mounting structure of the electronic component, and a process for producing the electronic component. Specifically, the present invention relates to an electronic component having a structure in which external electrodes are disposed on surfaces of the electronic component, a mounting structure of the electronic component, and a process for producing the electronic component.
2. Description of the Related Art
An example of ceramic electronic components each having a structure in which external electrodes are disposed on surfaces of a ceramic element is an electronic chip component, such as a multilayer ceramic capacitor, having a structure including a plurality of internal electrode layers 52a and 52b alternately disposed; ceramic layers 53, each internal electrode layer 52a being disposed opposite the corresponding internal electrode layer 52b with a corresponding one of the ceramic layers 53 provided therebetween; a ceramic laminate 51 having end surfaces 54a and 54b, the internal electrode layers 52a being connected to the end surface 54a, and the internal electrode layers 52b being connected to the end surface 54b; and a pair of external electrodes 55a and 55b, the external electrodes 55a and 55b being disposed on the end surfaces 54a and 54b, respectively, and being connected to the internal electrode layers 52a and 52b, respectively, as shown in FIG. 9. See, for example, JP 2001-210545.
In this multilayer ceramic capacitor, JP 2001-210545 discloses that the external electrode 55a includes a sintered electrode layer 56a, a Ni plating layer 57a disposed on the sintered electrode layer 56a, and a Sn plating layer 58a; and the external electrode 55b includes a sintered electrode layer 56b, a Ni plating layer 57b disposed on the sintered electrode layer 56b, and a Sn plating layer 58b. In general, the Ni plating layers 57a and 57b are arranged to prevent solder leaching of the sintered electrode layers 56a and 56b. The Sn plating layers 58a and 58bare arranged to improve solder wettability.
In view of the prevention of environmental pollution, lead-free solder has recently been used for mounting of electronic components. An example of the lead-free solder is Sn—Ag—Cu-based lead-free solder containing Zn.
In the case where a multilayer ceramic capacitor including external electrodes each having the above-described structure is mounted with the lead-free solder containing Zn, the diffusion of Zn into Ni plating layers constituting the external electrodes causes the formation of voids functioning as paths for the penetration of water and the like into the Ni plating layers. Furthermore, the elimination of Zn contained in the lead-free solder, i.e., the diffusion of Zn into the Ni plating layers, causes the formation of voids in soldered portions (lead-free solder) after soldering, the voids functioning as paths for the penetration of water.
As a result, the moisture resistance of the multilayer ceramic capacitor mounted on a mounting object, such as a circuit board, is reduced to disadvantageously degrade reliability.